One method of determining geometric errors in machines is known from WO2005/019769, in which the machine is operated to move a back-reflector within the measuring volume along a three-dimensional grid oriented with respect to the coordinate axes, and successive grid points are acquired. The reflector is tracked by an optical tracking device or “laser tracer” located on the machine bed and comprising an interferometer; the actual distance between each acquired grid point and a predetermined reference point associated with the laser source is measured interferometrically; as is known, this distance can be determined short of the dead path of the interferometer, which is unknown.
The same sequence of operations is performed with the tracer laser in different positions on the measuring machine bed.
On the basis of a kinematic model of the machine, the acquired-point coordinates and the distances measured by the interferometer are processed to calculate error parameters of the machine.
The known method described briefly above has the drawback of requiring an extremely precise, and therefore complex, high-cost, laser tracer capable of making continuous interferometric measurements alongside variations in orientation of the laser beam.
Moreover, for each position of the laser tracer, it introduces additional unknowns in the form of the dead path of the interferometer, and the laser tracer position.